This invention relates to the machine cutting of fabric or other sheet material, spread on a supporting surface, by means of a reciprocating cutter blade reciprocated along a reciprocation axis generally perpendicular to the sheet material while the blade is in cutting engagement with the material and moved forwardly along a desired line of cut, and deals more particularly with the construction of a blade used for such cutting and with a related method for using and sharpening the blade.
As to its construction, the blade of this invention in at least one of its aspects is of the general type shown in U.S. Pat. No. 4,653,373 wherein the base material of the blade at least in the vicinity of the cutting edge is covered with a thin coating of hard material which after sharpening of the blade is located at and defines the cutting edge so as to make the cutting edge more enduring and wear resistant than if defined by the softer base material. The present invention involves an improvement of the basic blade construction shown by said patent and also involves an improvement in its method of use.
In cutting machines controlled by automatic controllers, the cutting edge of the cutting blade before use of the blade is usually located on a reference plane passing through the middle of the blade thickness and then, as the blade is used, during sharpening cycles both sides of the blade are ground to maintain the cutting edge on the reference plane. In the blade shown by the aforesaid patent, however, the cutting edge is initially approximately on the reference plane and then during use of the blade only one side of it is sharpened by grinding, so that as a result of repeated sharpenings the cutting edge gradually moves further and further away from the reference plane. The blade thus cuts with precise accuracy only when first installed in a cutting machine and gradually loses such precise accuracy during the course of its service life. Further, when the blade is first installed the shape of the blade is generally symmetrical with respect to a first front to rear plane passing through the cutting edge so that the lateral forces imposed by the sheet material being cut on the blade are basically balanced and do not tend to laterally deflect the blade: but as the blade is repeatedly sharpened this symmetry and balance are gradually lost. That is, the blade has two inclined surfaces facing generally forwardly relative to the line of cut and which meet to define the cutting edge. Initially, these surfaces are substantially of equal size so that the lateral components of the forces exerted on them substantially sharpened from one side one of these surfaces grows in size while the other diminishes in size, causing a concomitant unbalancing of the lateral force components imposed on the blade by the material being cut through the surfaces.
Further, the service life of the blade shown in the aforesaid patent is restricted by the fact that the blade can be used and sharpened only throughout the period during which the cutting edge moves from the reference plane to some limit of displacement from the reference plane.
The general object of this invention is therefore to provide an improved blade, which may be hard coated, and a related method of using the blade, whereby the blade is capable of cutting with acceptable accuracy throughout a much longer service life than the service life of previously known blades of the same general type.
Another object of the invention is to provide a blade of the foregoing character wherein the lateral forces imposed on the blade by the sheet material being cut remain basically balanced throughout the service life of the blade.
Other objects and advantages of the invention will be apparent from the following description of a preferred embodiment of the invention and from the accompanying drawings and claims.